Devices for modulating the propagation of electromagnetic radiation represent fundamental building blocks for many modern technologies. Where a single spatial dimension is involved, such as in the propagation of an optical signal down an optical fiber, such modulation is commonly achieved by devices affecting the amplitude of the propagating light (e.g., OFF/ON). In that environment, one-dimensional electrooptical modulators are often used that are based on electrooptic and/or magnetooptic materials such as calcite, quartz, and lithium niobate that change their refractive index responsive to applied control signals, the materials being arranged into Mach-Zehnder interferometers (MZIs) or similar devices converting induced phase changes into amplitude changes by interference effects. Other one-dimensional electrooptical modulators include electroabsorption modulators variably absorbing the incident signal according to an applied electric field, and acoustic wave modulators using high-frequency sound traveling within a crystal or a planar wave guide to deflect light from one place to another.
Where two spatial dimensions are involved, e.g., in the controlled propagation of optical wavefronts in imaging systems, devices for temporal control of the propagating radiation include liquid crystal-based spatial light modulators (SLMs) and microelectromechanical (MEMs)-based SLMs, each generally providing for pixelwise amplitude or phase modulation of the propagating radiation. For static cases (i.e., no temporal control), incident optical wavefronts can be modulated by interferometrically recorded holograms of various kinds, including amplitude holograms recorded onto high-resolution photographic emulsions and phase holograms recorded onto photoresists or dichromated gelatins.
For any particular radiation modulation scheme, fundamental issues often arise with regard to one or more of spatial resolution, modulation depth, modulation speed, scalability to different wavelength regimes, amenability to computer control, and independence between amplitude and phase control. Moreover, practical issues often arise with regard to one or more of materials cost, materials availability, fabrication cost, durability, drive circuitry requirements, power consumption, device size, heat dissipation, and noise performance. Other issues arise as would be apparent to one skilled in the art in view of the present disclosure.